The gamma ray scintillation camera is the instrument of choice for imaging both static and dynamic radioisotope distributions in vivo. Radionuclide imaging conducted using gamma cameras is used to obtain information about functionality, morphology, and metabolic activity. Gamma cameras are used in investigation of cardiac activity, renal function, bone tumors, pulmonary emboli, liver metastasis, brain tumors, and thyroid pathology. The overall performance, size, weight, and cost of these cameras are strongly influenced by the photomultiplier tubes used in their construction. In particular, the low quantum efficiency, high cost, and bulkiness of PMTs are limiting factors in such gamma cameras. In view of these limitations, the goal of the proposed project is to investigate a novel design of silicon avalanche photodiodes which can intrinsically provide position sensing capability. These new position sensitive APDs require minimal electronic readout (and associated power) requirements and can provide high energy and spatial resolution. The goal of the proposed project is to investigate a high-resolution gamma camera design based on such devices. The Phase I project will be aimed at demonstrating the feasibility of the proposed approach. PROPOSED COMMERCIAL APPLICATION: Nuclear medicine including gamma camera, positron emission tomography, and single photon emission computed tomography, radiology, non-destructive testing, materials research, X-ray diffraction, nuclear and high energy physics research, astronomy, and geological exploration.